Kawasaki Mule SX Problems & How to Fix Them

Kawasaki Mule SX Problems

Off-roading is an exhilarating experience. Riding through mud, over rocks, and up hills on an ATV or UTV brings a sense of freedom and adventure. However, even the most rugged machines like the Kawasaki Mule SX can run into problems from time to time that sap the fun out of your ride.

So what are some of the most common Kawasaki Mule SX problems owners run into, and how can you diagnose and fix them yourself? Oftentimes, Mule SX issues can be addressed without taking your machine to the shop if you know what to look for. This guide will overview the major issues that afflict the Mule SX and provide tips to get your trusty side-by-side back up and running.

Fuel Delivery Issues

Many problems with the Mule SX originate from the fuel delivery system. Without proper fuel supply, the engine can sputter, stall, or fail to start altogether. Here are the key components of the fuel system to inspect if you are having issues:

Fuel Pump

The fuel pump is responsible for drawing fuel from the tank and sending it to the carburetor or fuel injectors. A failed fuel pump will cause starting problems or cause the engine to stall shortly after starting. Here are the signs of fuel pump failure:

  • Engine cranks but does not start
  • Engine starts but stalls out after a few seconds or minutes
  • Loss of power under load or at high RPMs

Verify the fuel pump is actually delivering fuel before condemning it. Check if fuel is reaching the carburetor when cranking the engine. No fuel present indicates a problem with the pump.

Replacing the fuel pump module assembly may be needed if it is determined the pump has failed. For fuel injected Mule SX models, ensure the fuel pump fuse has not blown before replacing the pump itself.

Fuel Filter

The fuel filter screens debris and contaminants from the fuel supply before it reaches the carburetor or injectors. Over time, residue can build up and clog the filter, restricting fuel flow. Symptoms of a blocked fuel filter include:

  • Difficult starts or stalling after starting
  • Reduced power when accelerating
  • Sputtering or coughing from fuel starvation

Luckily, the fuel filter is an easy and inexpensive part to replace. Locate the external in-line fuel filter and swap it out for a fresh one. Check that fuel flow has been restored afterwards.

Fuel Injectors

The fuel injectors on fuel-injected Mule SX models meter and spray atomized fuel into the engine. Clogged or dirty injectors disrupt this fuel mist, causing poor engine performance. Warning signs include:

  • Rough idle, stalling, misfires
  • Lack of power under acceleration
  • Black smoke from exhaust
  • Foul fuel smell

Using a fuel injector cleaning additive like Techron or Seafoam can help clean gummed up injectors and restore proper fuel flow. If cleaning fails, individual injectors may need replacement. Consult your owner’s manual on injector replacement procedures.

Loss of Power

A noticeable lack of the Mule SX’s characteristic zip and torque could indicate some underlying issues. If your side-by-side lacks its normal punch, look into these areas:

Air Filter

The air filter cleans intake air before it enters the engine. A clogged, dirty air filter prevents proper airflow, resulting in a lean fuel mixture and performance loss.

  • Inspect the air filter element after difficult rides in dusty/muddy conditions
  • Replace the filter if it appears excessively dirty or is covered in residue
  • Use compressed air to blow dust out of the filter after gentle tapping/brushing
  • Re-oil foam pre-filters after cleaning

Swapping in a fresh, clean air filter can restore power loss caused by restricted airflow. Just don’t remove the filter entirely, as this allows damaging dirt into the engine.

Spark Plugs

Spark plugs provide the spark required to ignite the air/fuel mixture in the combustion chamber. Old or fouled plugs have weak sparks, leading to performance issues like:

  • Lack of high-end power
  • Misfires, sputtering at speed
  • Difficult starts

Check the spark plugs after heavy riding or if power loss persists. Look for excessively worn electrodes, heavy soot deposits, discoloration from overheating, or oil fouling. Replacing worn plugs with new ones gapped to factory specs will refresh performance.

Inspect the ignition system wiring, coil, and stator as well if the new plugs misfire. A weak ignition system struggles to ignite the air-fuel mixture.

Engine Compression

If the Mule SX’s cylinders can’t properly contain the air-fuel mixture under compression, combustion and power output will suffer. Worn piston rings, leaking head gaskets, and blown head gaskets all lower compression. Symptoms include:

  • Significant loss of power
  • Misfires or ticking sounds from cylinders
  • Increased exhaust smoke
  • Overheating issues

Take the Mule to a dealer to have a compression test performed if internal engine damage is suspected. Low compression usually necessitates an engine rebuild or new cylinder.

Overheating Woes

Engine overheating is never something to ignore as it can quickly lead to catastrophic engine damage. Here are some common reasons for Mule SX overheating issues and how to address them:

Coolant Leaks

Your Mule SX relies on liquid-cooled forced induction to manage engine temperatures. Coolant leaks either externally or internally from damaged hoses, a cracked radiator, or failed water pump will cause overheating and should be addressed immediately.

Check under the Mule after riding for any coolant leaks near hoses, radiator, water pump, thermostat housing, or reservoir. Top off any lost coolant and replace faulty cooling system components to prevent further leaks leading to overheat conditions.

Cooling Fan

If the Mule’s cooling fan stops working, it cannot dissipate heat away from the radiator. Monitor the fan during riding and check for any of these issues:

  • Fan not activating when engine gets warm
  • Intermittent fan operation
  • Lack of airflow from fan failure
  • Blown fuse disabling the fan

Replace any seized-up or failed fan assemblies. The cooling fan circuit may need wiring repairs if a faulty motor is ruled out. Verify the fan relay and temperature sensor are working correctly as well.

Clogged Radiator

Air needs to flow freely through the radiator fins in order for it to effectively cool the Mule’s engine. Mud, debris, and dead bugs can obstruct the radiator over time, leading to cooling issues and higher operating temperatures.

Carefully clean the radiator fins with compressed air or a pressure washer if you notice any blockages. Avoid damaging the delicate fins in the process. Catching and clearing obstructions early keeps the radiator working at max efficiency. Don’t ride if the radiator is excessively plugged as overheating can quickly result.

Other Common Problems

Beyond the major issues above, here are some other frequent Mule SX trouble spots and how to tackle them:

Battery Issues

Electrical charging problems, bad cell, or aging can cause the Mule’s battery to die unexpectedly. Some signs of a weak battery include:

  • Dimming headlights at idle
  • Difficulty turning over the starter
  • Battery draining prematurely

Recharge the battery and clean any corroded terminal connections. Check the stator and regulator/rectifier that supply the charging system if issues continue. Replace the battery if it still struggles to hold a charge.

CV Boot Failures

The CV boots on the Mule’s AWD axles protect the vulnerable joint but tear easily when ripped by rocks or vegetation. Torn boots lead to rapid grease loss and eventual axle failure.

Inspect boots after challenging rides and look for ripped rubber or grease splatter. Replace any damaged boots before contamination ruins the axles. Catching tears early greatly extends the life of the axles.

Belt Wear

The drive belt connecting the engine to the transmission experiences high loads and wear during riding. Signs of a worn drive belt include squealing on acceleration (especially uphill), lack of top speed, and belt residue.

Adjust the belt tension per the owner’s manual if slack. Otherwise replace excessively worn belts before they snap and leave you stranded. Checking belt condition at regular service intervals avoids unexpected failure.


While UTVs like the Mule SX are designed to handle tough riding, problems can sneak up over time that hamper your trail adventures. Paying attention to potential issues and knowing savvy DIY fixes can reduce downtime and costly shop visits. Reference this guide covering common Kawasaki Mule SX problems to quickly troubleshoot and address any performance-sapping issues that occur.

Performing routine maintenance and not ignoring warning signs of impending problems will keep your trusty Mule SX running great for the long haul. With a reliable side-by-side partner, you can confidently set out to conquer your next backcountry excursion.

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